Electric vehicles and hybrid vehicles are provided with a hot-water heating device for heating the passenger compartment. Specifically, they are provided with a water circulation passage, at one position of which water is heated to be hot water by a heater (water-heating heater) and at another position (downstream side) of which heat exchange is performed by a heat exchanger between the hot water and air blown to the passenger compartment, to thereby obtain hot air for heating the passenger compartment.
The power supply of such a heater is a high-voltage power supply, and thus, the heater is used at high voltage and high current. Therefore, there is a possibility that abnormal overheating is generated in the heater for some reason, and thus, overheating protection is required.
In Patent Document 1, the temperature of a heater (including the temperature of hot water obtained by the heater) is measured, and if the temperature of the heater exceeds a predetermined value, forcibly turn off a switch for ON and OFF of the voltage supplying to the heater and maintain such an OFF-state.
In Patent Document 2, a temperature fuse is disposed in the heater energizing circuit so as to be in series with the heater, and the temperature fuse is melted when the heater is abnormally overheated. When high power is applied thereto, the temperature fuse does not have sufficient reliability, and thus, multiple heaters are connected in parallel, and the temperature fuse is provided for each heater so as to operate the temperature fuses at low power (low current).